1. Field of the Invention
The present invention relates to an image capturing apparatus and image processing method for processing a pixel output from an image sensor which detects a focus state by using some pixels as phase difference focus detection elements.
2. Description of the Related Art
For example, Japanese Patent No. 3592147 has proposed an image capturing apparatus which detects a focus state by using some pixels of an image sensor as focus detection elements. In the image capturing apparatus disclosed in Japanese Patent No. 3592147, some pixels of an image sensor are set as focus detection pixels. Subject beams having passed through different pupil regions symmetrical with respect to the center of the optical axis of a photographing lens are formed into images on a plurality of focus detection pixels. The phase difference between these subject beams is detected to detect the focus state of the photographing lens.
A partial region of the focus detection pixel is shielded from light. Hence, a pixel output from the focus detection pixel is a pixel output of attenuated light in comparison with a normal pixel. It is known that the light attenuation amount in the focus detection pixel changes depending on optical characteristics regarding the focus detection pixel. In an image capturing apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2010-62640, a pixel output from a focus detection pixel is corrected by gain adjustment, or corrected by using pixel outputs from pixels around a focus detection pixel.